The present invention relates to a display processing apparatus, and more particularly to a display processing apparatus including memory means in which pattern information to be displayed is stored and means for addressing the memory means to select the pattern information to be displayed.
Heretofore, a digital processor (e.g. a microprocessor, a display controller) has been used for the purpose of displaying a character pattern (such as letters, digits, symbols, marks or figures) on a display device, e.g. a CRT (cathode ray tube), LCD (liquid crystal display), and PDP (plasma display panel). Character pattern data to be displayed is preliminarily stored in a memory in the form of digital code and is read out of the memory by means of an addressing means of the digital processor. The read out character pattern data is sent to a display device, and is displayed at a designated position of a screen. Different types of signals are used in accordance with display devices for designating a position at which a character pattern is displayed. For instance, vertical and horizontal raster scanning signals are used in a CRT device, and digit and segment signals are used in an LCD device. In order to accurately display a character pattern at a designated position of a screen, these signals must be synchronized with a character pattern data to be sent to a display device. Therefore, it is preferred to simplify the coupling between the memory and the display device.
On the other hand, character pattern data is stored in a memory so as to have a predetermined pattern size. Accordingly, the size of the character pattern is always constant on a screen. Changing the size is very difficult while still keeping the aforementioned synchronous relation between the character pattern data and the signals for designating the display position. Consequently, the display processing apparatus of the prior art has the following shortcomings:
1. Since the change in size of a character pattern on a display screen is impossible, increase or decrease of a number of character patterns which can be displayed on a screen is also impossible. PA0 2. Since intervals between vertically or horizontally consecutive characters cannot be changed, in the case whereby especially complex characters appear consecutively to each other, it is difficult to identify the respective characters. PA0 3. In order to display a character pattern with a different size, another memory in which the character pattern data is prepared according to the different size is necessitated; and therefore, memory capacity is greatly increased. PA0 4. It is possible to provide a circuit with a high degree of operation capability, such as function oprations between a memory and a display device, so that character data read out of the memory may be input to that circuit to carry out magnification or reduction of character size. However, this circuit is both complex and expensive. In addition, although the timing of read-out of character data and its display on a screen can be synchronized in a relatively simple manner, in the above-mentioned case the synchronization between the timing of read-out and the timing of display becomes difficult to achieve, because the operations must be effected between the memory and the display device. As a result, flickering or deviation of display is likely to occur.